1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a phase shifter, a method of fabricating the same, and a duplexer having the same. More particularly, the present invention relates to a phase shifter capable of changing the phase of a transmitted/received signal by using an inductor and a capacitor, a method of fabricating the same, and a duplexer having the same.
2. Description of the Related Art
A duplexer is a representative element that uses filters and serves to efficiently share one antenna by properly branching transmitted/received signals through the antenna. Such a duplexer is a major component of a mobile communication device, such as a cellular phone. The duplexer branches a transmitted signal and a received signal in a communication system that concurrently transmits and receives a signal.
The duplexer basically includes a transmitting-end filter and a receiving-end filter. The transmitting-end filter is a band pass filter that passes only a frequency subject to transmission, and the receiving-end filter is a band pass filter that passes only a frequency subject to reception. By passing specified frequency band signals through the respective filters, one antenna can efficiently be shared.
Meanwhile, since the frequencies of signals transmitted/received through the transmitting-end filter and the receiving-end filter are slightly different from each other, they sensitively react to each other to cause a signal interference to occur between them. To solve this, it is conventional that the duplexer is additionally provided with a phase shifter for isolating the transmitting/receiving-end filters from each other. One example of a related art duplexer with the phase shifter is shown in FIGS. 1 to 3.
Referring to FIGS. 1 and 2, a related art duplexer includes a phase shifter 30, a transmitting-end filter 10, and a receiving-end filter 20. The phase shifter 30 includes an input port 31a connected to the transmitting-end filter 10, an output port 31b connected to the receiving-end filter 20, and an inductor 32 and a capacitor 33 interposed between the input port 31a and the output port 31b. The input port 31a and output port 31b are provided on a substrate 31.
Referring to FIG. 3, the inductor 32 and the capacitor 33 are separately formed on the substrate 31 through separate processes. More specifically, the inductor 32 includes a lower connection 32a, an insulation layer 32b, and a coil forming portion 32c which are deposited on the substrate 31 in order. The lower connection 32a and the coil forming portion 32c are connected to each other through a via hole 32d formed on the insulation layer 32b, so that the inductor 32 is electrically connected to each of the ports 31a and 31b. 
The capacitor 33 includes a lower electrode 33a, an insulation layer 33b, and an upper electrode 33c, which are deposited on the substrate 31 in this order.
The capacitor 33 is deposited and formed between the inductor 32 and the substrate 31, as shown in FIG. 2. Specifically, after the capacitor 33 is deposited on the substrate 31, the inductor 32 is then deposited on the capacitor 33. The upper electrode 33c of the capacitor 33 is grounded to the exterior through a connection pad 41, an insulation layer 42, and a ground electrode 43, which are deposited on the upper electrode 33c in this order.
A complex process of depositing six structures in total is needed in a range in which the capacitor 33 and the inductor 32 are superposed on the substrate 31. As such, a process of fabricating the phase shifter 30 is complicated, and the size of the phase shifter 30 is increased. Consequently, it is difficult to reduce the size of the duplexer.